[py] Fix flaky test_output_buffer_flushes_at_default_size_limit#6585
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The test polled total_completed_records, which can freeze below the 10M size cap. This happens when a multi-step transaction produces output across multiple steps. The first output pushes buffer size beyond the 10M limit, but doesn't increase processed record count. The remaining outputs never flush because the default time cap is infinite, so the processe record count never reaches the cap and the test times out. Poll the sink's transmitted_records instead. The endpoint updates this counter after the Delta Lake commit succeeds, so it crosses the cap exactly when the size-cap flush completes, independent of completed-record accounting. Signed-off-by: Leonid Ryzhyk <ryzhyk@gmail.com>
mihaibudiu
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Jul 3, 2026
mythical-fred
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Jul 3, 2026
mythical-fred
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Approve. Clean fix — polling the sink's transmitted_records sidesteps the multi-step-transaction completed-count freeze, and the updated docstring matches the new invariant. Test still asserts the same behavior (>= 10M records reach the sink), just via a counter that actually advances.
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The test polled total_completed_records, which can freeze below the 10M size cap. This happens when a multi-step transaction produces output across multiple steps. The first output pushes buffer size beyond the 10M limit, but doesn't increase processed record count.
The remaining outputs never flush because the default time cap is infinite, so the processed record count never reaches the cap and the test times out.
Poll the sink's transmitted_records instead. The endpoint updates this counter after the Delta Lake commit succeeds, so it crosses the cap exactly when the size-cap flush completes, independent of completed-record accounting.